Purposes: The purposes of this project were to: (1) develop a better standardized and computerized method of visual acuity testing for clinical research as an alternative to the Early Treatment for Diabetic Retinopathy Study (ETDRS) testing protocol, and (2) evaluate the measurement properties (stability, test-retest reliability, and concordance) of the novel system relative to the ETDRS protocol. Design: Multi-center observational study. Methods: We measured visual acuity on 265 subjects at three clinical centers with both the electronic visual acuity testing system (E-ETDRS) and the standard ETDRS protocol (S-ETDRS). Acuity thresholds were estimated twice on one eye of each subject. E-ETDRS testing was conducted using the Electronic Visual Acuity Tester (EVA), which utilizes a programmed Palm (Palm, Inc, Santa Clara, California) handheld device communicating with a personal computer and 17-inch monitor at a test distance of 3 meters. We assessed test-retest reliability and concordance with correlation analyses. We assessed stability and performance differences in repeated acuity measures with linear mixed models. Mixed models adjust for covariance in replicated within-subjects factors. Our within-subjects factors included test type (S-ETDRS v. E-ETDRS) and test order. Between subjects factors included test site, diagnosis (normal, retinal diagnosis, other diagnosis), and age. We assessed testing efficiency on differences in test durations between EVA-ETDRS and ETDRS with t-tests. Results: For the E-ETDRS protocol, test-retest reliability was high (r = 0.99; with 98% of retests within 0.2 logMAR (10 letters) of initial test) and comparable to that of S-ETDRS testing (r = 0.99; with 98% of retests within 0.2 logMAR of initial test). The E-ETDRS and S-ETDRS scores were highly correlated (r = 0.96 for initial tests and r = 0.97 for repeat tests). Based on estimates of 95% confidence intervals, a change in visual acuity of 0.2 logMAR from a baseline level is unlikely to be related to measurement variability using either the E-ETDRS or the S-ETDRS visual acuity testing protocol. Adjusted mean acuity differences from the multivariable analyses are presented in the Table. The second administration of the E-ETDRS yielded acuity threshold estimates that were, on average, 1.6 letters better than those obtained with the first administration. This value is within the limits of normal within-subject variance. In no other instances did comparisons yield statistically significantly different acuity thresholds. Table. Adjusted* Mean Differences (95%CI) in Acuity Scores (ETDRS Letters) --------------------------------------------------------------------------- Comparison: S-ETDRS v. E-ETDRS, Mean = -0.14 (-1.00, 0.72),p=0.75 Comparison: S-ETDRS 1 v. S-ETDRS 2, Mean = 0.12 (-1.10, 1.33),p=0.85 Comparison: E-ETDRS 1 v. E-ETDRS 2, Mean = -1.61 (-2.82, -0.40),p=0.01 Comparison: 1st Test v. 2nd Test, Mean = -1.49 (-3.30, 0.23),p=0.09 Comparison: 1st S-ETDRS v. 1st E-ETDRS, Mean = -1.00 ( 0.21, 2.21),p=0.11 Comparison: Test Order (1st v. 2nd), Mean = -1.25 (-5.09, 2.95),p=0.53 --------------------------------------------------------------------------- Note: *Means are adjusted for test site, ocular diagnosis (normal, retinal disease, other ocular disease), and subject age. The E-ETDRS method demonstrated equivalent efficiency to the ETDRS method. The duration of testing between methods was not significantly different after adjusting for test site, subject diagnosis, and subject age. Conclusions: The E-ETDRS protocol has high test-retest reliability that is comparable to that of the S-ETDRS. The computerized method has advantages over the S-ETDRS protocol in that it: (1) ensures accurate and complete data recording and management, (2) requires single viewing distance for testing stimuli from 20/12(-0.2 logMAR) to 20/800(1.6 logMAR), (3) decreases potential for technician-related bias.